The idea that “rule of thumb” was named after an old law allowing a man to hit his wife with a stick no thicker than his thumb has been debunked as revisionist history, but that doesn’t change the fact that many of us rely on the commonly accepted rules every day. Here are a few of the highest rated ones that can be found in the database at RulesOfThumb.org. Choosing a barber: “Between two barbers in a shop, choose the one with the worst haircut. They cut each other’s hair.” Measurements: “A US bill is about six inches long.” Writing: “A list of three things always sounds better, even if you’re repeating yourself.”